Conventional articles of footwear often include two primary components: an upper and a sole structure. The upper provides a covering for the foot and securely positions the foot relative to the sole structure. The sole structure is secured to a lower surface of the upper and configured so as to be positioned between the foot and the ground when a wearer is standing, walking or running. Sole structures are often designed so as to cushion, protect and support the foot. Sole structures may also be designed so as to increase traction and to help control potentially harmful foot motion such as overpronation.
Many types of athletic footwear have a sole structure that includes a deformable midsole. A primary element of many conventional midsoles is a resilient polymer foam material that extends throughout the length of the footwear. The physical characteristics a conventional midsole often depend on the density and other properties of the polymer foam material and on the dimensional configuration of the midsole. By varying these factors throughout the midsole, the relative stiffness, degree of ground reaction force attenuation, and energy absorption properties may be altered to meet the specific demands of the activity for which the footwear is intended to be used.
Commonly-owned U.S. Pat. No. 6,990,755 describes an article of footwear having an articulated sole structure in which multiple sipes separate discrete sole elements of the midsole. The resulting sole structure helps to simulate a sensation of barefoot running while at the same time providing a degree of cushioning and protection to the wearer foot. The motion of a human foot during running and other activities can be quite complex, however. Accordingly, there remains an ongoing need for improved articulated sole structures that better accommodate natural tendencies and kinematics of the human foot.